The smooth bark of small red maples makes this species ideal for buck rubs in the forests of the mid-eastern United States.

美国中东部森林中的树皮光滑的小红枫是雄鹿进行摩擦的理想树种。

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The birch has smooth bark and slender branches.

桦树有光滑的皮和细长的枝。

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I feel the delicate symmetry of a leaf. I pass my hands lovingly about the smooth skin of a silver birch, or the rough shaggy bark of a pine.

我感到树叶的对称美，用手摸着白桦树光滑的树皮或是松树那粗糙的厚厚的树皮。

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In younger ash there is a distinctive smooth silver grey bark and sooty black buds.

BBC: The heartbreak of watching the slow death of ash trees